The aim of our project is to learn more about the structure of immunoglobulin messenger RNAs (mRNAs) and the arrangements of immunoglobulin (Ig) genes, using mouse myleomas as a model system. In the preceding grant period, we have determined 5'-terminal sequences in myeloma mRNAs, purified mRNAs for three kappa light chains and for mu and alpha heavy chains, compared translation of Ig mRNAs in three cell-free systems, demonstrated a 'capped' 5'-end and modified nucleoside in an Ig kappa mRNA and determined a 100-residue non-coding sequence at its 3'-end, developed a procedure for isolation of specific polysomes, and established the linkage of the mouse rRNA genes. In the coming period, we plan to use recombinant DNA to facilitate structural studies on Ig mRNAs and genes. Complementary DNA copies of representative Ig mRNAs will be inserted into bacterial plasmids; the inserts will then be excised and fragmented for sequence analysis. The cloned sequences will also be used as hybridization probes to learn more about the number of Ig genes and as affinity reagents to aid isolation of Ig precursor RNAs. Restriction endonuclease mapping of mouse DNA will be used to examine the arrangement and presumed translocation of Ig genes. Enrichment methods will be explored to aid closing of cellular DNA containing Ig genes. These studies should contribute significantly to understanding of Ig biosynthesis and the general picture of mRNA structure.